Long-term tumor remission under trastuzumab treatment for HER2 positive metastatic breast cancer - results from the HER-OS patient registry

Background: In this study, we examined patients who had non-progressive disease for at least 2 years after diagnosis of inoperable locoregional recurrent or metastatic breast cancer under continuous trastuzumab treatment. Our primary goal was to assess the long-term outcome of patients with durable response to trastuzumab. Methods: 268 patients with HER2-positive inoperable locally recurrent or metastatic breast cancer and non-progressive disease for at least 2 years under trastuzumab treatment were documented retrospectively or prospectively in the HER-OS registry, an online documentation tool, between December 2006 and September 2010 by 71 German oncology centers. The study end point was time to tumor progression. Results: Overall, 47.1% of patients (95% confidence interval (CI): 39.9-54.1%) remained in remission for more than 5 years, while the median time to progression was 4.5 years (95% CI: 4.0-6.6 years). Lower age (< 50 years) and good performance status (ECOG 0) at time of trastuzumab treatment initiation as well as complete remission after initial trastuzumab treatment were associated with longer time to progression. Interruption of trastuzumab therapy correlated with shorter time to progression. Conclusions: HER2-positive patients, who initially respond to palliative treatment with trastuzumab, can achieve a long-term tumor remission of several years.